Breast cancer screenings cost Medicare $1.08 billion annually, lead researcher Dr. Cary Gross and his team at the Yale School of Medicine found. Given that Medicare spends $1.36 billion a year on breast cancer treatment, Gross said he expected the screenings costs to be much lower.

"It should be a call to do further research to identify the best screening strategy," Gross said. "If we're spending more, does it really help the patients?"

Click here to read about the married research couple that both got breast cancer.

Gross said his study can't conclude whether mammograms are effective, but it does take a good look at where the money is going to prompt further study.

Gross and his colleagues also found that areas where people spent more money on breast cancer screenings didn't have better outcomes than those that didn't. However, the study was somewhat limited because it only followed up with patients for two years.

"You could argue when it comes to screening, that if you invest more in screening, maybe you'll spend less in treatment," he said. "But we didn't find that."

About $410.6 million of the total screening costs went toward women over 75 years old, a controversial age group because of a 2009 United States Preventative Services Task Force recommendation that said older women might not benefit from the screenings.

However, the American Cancer Society and several other medical organizations ignored the USPSTF recommendations because they drew different conclusions from the data, said Dr. John Huff, the imaging director of the Vanderbilt Breast Clinic in Tenn. Huff did not work on the study.

The American Cancer Society still recommends annual breast cancer screenings for women over 40.

"I think the biggest question is not so much the cost, which we certainly need to be aware of, but the question of what we get for that cost and what value we place on what we get," Huff said, addressing over-diagnosis and over-treatment.

Not unlike slow-growing prostate cancer that doesn't always require treatment, some breast cancers might not need surgery, chemotherapy and radiation, Huff said. But before the medical community can determine whether over-diagnosis and over-treatment is at play, it must find a way to determine which patients have slow-growing breast cancers and which don't.

"There are some breast cancers that might not need aggressive treatment, but we unfortunately are currently unable to identify which ones they are," Huff said. "So it's nice to say we might be over-diagnosing or over-treating, but until we have evidence that helps us understand which people those are, it's hard to separate those out as a group. So we're left being a little less targeted."

Huff explained that some 75-year-old women could benefit from breast cancer screenings because they could live another 15 years. But other 75-year-olds might be in very poor health and have what medical professionals call "co-morbidities," meaning they could die from other health problems and therefore benefit very little from breast cancer screening.

Huff said there are many pieces to the Medicare and breast cancer screening puzzle and that one study alone isn't enough to convince him that guidelines need to change.

"What we all need to do with this piece is put it in place with the rest of them and continue to investigate these things and try to establish as much knowledge and evidence that we can as that evolves," Huff said.